The experiments described in this thesis were designed towards reaching an understanding of the control of flux through the arginine pathway in Neurospora crassa. The previous algebraic analysis of steady state enzyme networks has shown that the flux is a systemic property and that, typically, the relation between flux and effector is non-linear. It was therefore necessary in the present experimental analysis to apply the method of modulation, i.e. to determine the flux response to a series of changes in the concentration of a putative effector. It was already known that arginine affects the rate of each step in the arginine pathway by controlling the amount (induction or repression) and/or activity (activation or inhibition) of the individual enzymes. The principal and largely successful aim of this study, therefore, was to develop and apply an experimental method whereby the mycelial argtnine concentration could be predictably modulated over a wide range, under steady state conditions; then to monitor and interpret the systemic response, as indicated by the changes in i) the levels of other pathway intermediates, ii) the specific activities of the connecting enzymes and iii) the measured fluxes. This was achieved by controlling the rate of citrulline uptake and, consequently, the steady state concentration of mycelial arginine in the auxotrophic mutant ?. Ornithine then becomes an "end product" with its accumulated steady state concentration indicating the pathway flux. From the experimentally generated relationships between metabolic pools and between pools and enzyme specific activities the mechanisms of importance in the control of the pathway fluxes were revealed. It is shown that there is no unitary solution to the problem of flux control; a number of different mechanisms effect the control of flux through the arginine pathway with the proportion of the control exerted by each depending absolutely upon the level that the flux has.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660690 |
| Date | January 1979 |
| Creators | Porteous, David J. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11273 |
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